package com.googlecode.gwtbb.client.shared.util;

/**
 * Taken from http://www.javapractices.com/Topic28.cjp
 * <p/>
 * Collected methods which allow easy implementation of <code>hashCode</code>.
 * <p/>
 * Example use case:
 * <pre>
 *  public int hashCode(){
 *    int result = HashCodeUtil.SEED;
 *    //collect the contributions of various fields
 *    result = HashCodeUtil.hash(result, fPrimitive);
 *    result = HashCodeUtil.hash(result, fObject);
 *    result = HashCodeUtil.hash(result, fArray);
 *    return result;
 *  }
 * </pre>
 */
public final class HashCodeUtils {
	/**
	 * An initial value for a <code>hashCode</code>, to which is added contributions
	 * from fields. Using a non-zero value decreases collisons of <code>hashCode</code>
	 * values.
	 */
	public static final int SEED = 23;


	/// PRIVATE ///
	private static final int fODD_PRIME_NUMBER = 37;

	public static int hash(int aSeed, boolean aBoolean) {
		return firstTerm(aSeed) + (aBoolean ? 1 : 0);
	}

	public static int hash(int aSeed, char aChar) {
		return firstTerm(aSeed) + (int)aChar;
	}

	public static int hash(int aSeed, int aInt) {
		/*
			* Implementation Note
			* Note that byte and short are handled by this method, through
			* implicit conversion.
			*/
		return firstTerm(aSeed) + aInt;
	}

	public static int hash(int aSeed, long aLong) {
		return firstTerm(aSeed) + (int)(aLong ^ (aLong >>> 32));
	}

	public static int hash(int aSeed, float aFloat) {
		return hash(aSeed, (long)aFloat);
	}

	public static int hash(int aSeed, double aDouble) {
		return hash(aSeed, (long)aDouble);
	}

	public static int hash(int aSeed, Object aObject) {
		int result = aSeed;
		if (aObject == null) {
			result = hash(result, 0);
		} else {
			result = hash(result, aObject.hashCode());
		}
		return result;
	}

	private static int firstTerm(int aSeed) {
		return fODD_PRIME_NUMBER * aSeed;
	}
}
